Observer-based studies often underestimate key ecological parameters. Here a fresh approach
was used to analyse six years (2006–11) of attendance cycles to estimate foraging trip lengths of a
lactating flipper-tagged otariid: subantarctic fur seals at Marion Island. Multi-state mark-recapture
models were used to calculate detection failures of females, correct estimates accordingly, and investigate
the effects of year, season, pup sex and the presence of a telemetry device on attendance cycle parameters.
There were no differences between corrected and uncorrected attendance data. This is attributed to the
high capture probability across all seasons (range: 83–98%). This illustrates that observer-based studies
are useful to augment telemetry studies. Only season and pup sex had a significant impact on female
provisioning rates. In winter, foraging trip durations were longer (t-value = 25.22, P <0.0001) and
attendance durations shorter (t-value = -2.15, P = 0.01) than during summer. Females with female pups
spent a higher proportion of their time on land (χ2 = 6.6, P < 0.05). Male pups have higher growth
demands and are larger which suggests they can deplete female milk-stores faster.